1. Field of the Invention
The present invention relates to image processing apparatus, a method of processing image data and a data carrying medium.
2. Description of the Related Art
The digitisation of image processing has enabled many new image manipulation techniques to be developed. Available digital processing effects include a process of color warping, in which color attributes of an image, or area of an image, can be modified in some way. Common uses for such a technique are removal of unwanted color artefacts, special effects and control over aesthetics.
Many image processing systems provide control over color through the use of gamma correction curves. Gamma correction curves define transfer functions that are applied to red, green and blue image data values, in such a way that a color transformation occurs. However, manipulation of such curves to produce satisfactory results is extremely difficult. In the case of creating special effects, the lack of intuitive feel of such an approach makes such an approach extremely limited.
From a mathematical perspective, many systems provide color transformations defined in terms of matrices. Matrices may be used to define arbitrary transformations in color space, just as they are used in the more familiar world of computer modelling and computer-aided design. However, although such techniques theoretically provide an enhanced level of control over color space, and have the potential to provide useful color warping tools, the lack of an intuitive relation between the mathematics and the effect upon the colors of an image makes these techniques difficult to apply.
In particular, a common requirement in image processing is to change one particular color in an image, for example, to modify the blue color of the sky, or the green color of an apple. These are requirements that are easily stated in artistic terms. However, known image processing tools are restricted in their ability to provide an appropriate interpretation of the artist""s intention in these cases.
According to an aspect of the present invention, there is provided apparatus for processing image data, comprising storage means arranged to store instructions, memory means for storing said instructions during execution and for storing image data, processing means for performing image processing in which said image data is processed to modify color values, and display means for facilitating user interaction with said image processing, wherein said processing means is configured such that, in response to said instructions, said image data is processed by steps of: identifying a source color; identifying a destination color; identifying three fixed points in color space; identifying a source color volume defined by said source color with said three fixed points; identifying a destination color volume defined by said destination color and said three fixed points; and defining a correspondence transformation between said source and said destination color volumes and applying said correspondence transformation to said image data.